1. Field of the Invention
This invention relates to a simple, inexpensive, apparatus for taking a continuous readout of a distributed temperature field. An example of such a temperature field is the temperature profile of the ocean. The apparatus lends itself readily to use on stationary and moving platforms, operating on the surface or submerged.
The construction of the distributed temperature sensor is based on an electromagnetic transmission line, in the form of a coaxial cable. Such a transmission line exhibits a characteristic impedance Z.sub.0 for electromagnetic signals that is dependent on the transversal dimensions of the conductors and also on the electromagnetic properties of the insulating material between the two conductors, such as the dielectric constant .epsilon. and the permeability .mu.. If these electromagnetic properties are temperature-dependent and the transmission line is immersed into a medium with spatially varying temperatures, the characteristic impedance of the transmission line will undergo local variations. These variations can be detected and localized with a time domain reflectometer.
2. Description of the Prior Art
Currently there are two principal devices in use for recording temperature profiles of the ocean.
The first is the bathythermograph. It is part of the standard equipment of most commercial and naval platforms. Its mode of operation is so widely known that a detailed description is not considered to be necessary. The device is expendable and is capable of providing a single temperature profile plot at a time.
The second prior art device is the thermistor chain. Its use is considerably less widespread than that of the bathythermograph, mainly because of its higher degree of complexity, greater cost and substantial difficulties in handling and maintenance. It consists of a large number of closely spaced electrical temperature sensors (thermistors) mounted on a steel chain that is trailed behind a moving platform. A heavy weight at the lower end holds the chain in a nearly vertical position while the towing platform is in motion. The electrical signals of the individual temperature sensors are either hardwired or telemetered to a processing system on board the platform. Because of its weight, length, bulkiness and relative fragility, it requires heavy winch equipment as well as utmost care in handling during deployment, towing, and recovery operations.
In contrast to the bathythermograph, the thermistor chain is capable of providing a continuous readout of the temperature profile. If required, however, this can be approximated by the bathythermograph at the cost of expending a large number of probes in sequence. If continuous readout of the temperature profile or a close approximation of it is the requirement, the cost will be high and the procedure complicated with both prior art devices.
One of the main advantages of the invention is that it provides a continuous readout of a temperature field with a device substantially less complicated than conventional devices used for measuring temperature profiles in the ocean. It can accomplish the same test for several orders of magnitude less cost. Because of the cable's inherently strong construction, it requires neither delicate handling nor extensive maintenance.